<?php

/**
 * @file
 * Provides a stub cache implementation to be used during installation.
 */

/**
 * Defines a stub cache implementation to be used during installation.
 *
 * The stub implementation is needed when database access is not yet available.
 * Because Drupal's caching system never requires that cached data be present,
 * these stub functions can short-circuit the process and sidestep the need for
 * any persistent storage. Obviously, using this cache implementation during
 * normal operations would have a negative impact on performance.
 */
class DrupalFakeCache extends DrupalDatabaseCache implements DrupalCacheInterface {

	/**
	 * Overrides DrupalDatabaseCache::get().
	 */
	function get($cid) {
		return FALSE;
	}

	/**
	 * Overrides DrupalDatabaseCache::getMultiple().
	 */
	function getMultiple(&$cids) {
		return array();
	}

	/**
	 * Overrides DrupalDatabaseCache::set().
	 */
	function set($cid, $data, $expire = CACHE_PERMANENT) {
	}

	/**
	 * Overrides DrupalDatabaseCache::clear().
	 */
	function clear($cid = NULL, $wildcard = FALSE) {
		// If there is a database cache, attempt to clear it whenever possible. The
		// reason for doing this is that the database cache can accumulate data
		// during installation due to any full bootstraps that may occur at the
		// same time (for example, Ajax requests triggered by the installer). If we
		// didn't try to clear it whenever this function is called, the data in the
		// cache would become stale; for example, the installer sometimes calls
		// variable_set(), which updates the {variable} table and then clears the
		// cache to make sure that the next page request picks up the new value.
		// Not actually clearing the cache here therefore leads old variables to be
		// loaded on the first page requests after installation, which can cause
		// subtle bugs, some of which would not be fixed unless the site
		// administrator cleared the cache manually.
		try {
			if (class_exists('Database')) {
				parent::clear($cid, $wildcard);
			}
		}
		// If the attempt at clearing the cache causes an error, that means that
		// either the database connection is not set up yet or the relevant cache
		// table in the database has not yet been created, so we can safely do
		// nothing here.
		catch (Exception $e) {
		}
	}

	/**
	 * Overrides DrupalDatabaseCache::isEmpty().
	 */
	function isEmpty() {
		return TRUE;
	}
}
